1. Field of the invention
The invention relates, in general, to air conditioning apparatus. In particular, the invention relates to a split-type air conditioning apparatus including a refrigerating circuit unit (external unit) installed outside a house and an air conditioning unit (internal unit) arranged inside the house.
2. Description of the related art
In the past, key factors considered in the design of air conditioning apparatus have been energy savings, comfortable performance, and ease of operation. In recent years, the audible sound generated from the air conditioning apparatus has been focused on as one of the factors adversely affecting the performance of the apparatus in terms of environmental quarity.
Japanese Laid-open patent 60-4741 discloses an air conditioning apparatus which controls the level of the audible sound generated by the air conditioning unit arranged inside the room. In this conventional air conditioning apparatus, a microphone is arranged in the air conditioning unit to detect audible sound in the room. The actual audible sound in the room is detected while the air conditioning apparatus operates. The actual audible sound is the total sound value of both the audible sound radiated from the air conditioning unit when the air conditioning apparatus operates and the background audible sound, which is the noise value in the room when the air conditioning apparatus stops. In the conventional air conditioning apparatus, an estimated background audible sound value is calculated by a specific equation based on the actual audible sound value detected by the microphone during the operation of the air conditioning unit. If the estimated background audible sound value is greater than a preset background audible sound value, the rotational speed of an internal fan device arranged in the air conditioning unit is decreased by a prescribed value to reduce the level of the audible sound radiated from the air conditioning unit.
In the above-described conventional air conditioning apparatus, the actual audible sound value during the operation of the air conditioning apparatus can be reduced. However, since the preset background audible sound value is constant, it is difficult to control the actual audible sound value in response to changes in the level of the background audible sound in the room, e.g., daytime, nighttime, etc.
In addition, in the conventional air conditioning apparatus, the control of audible sound radiated from the refrigerating circuit unit, which is arranged outside the house, is not considered. However, the audible sound radiated from the refrigerating circuit unit becomes an environment problem in an area crowded with many houses or apartments.